This invention relates to a method and device for continuously press-forming a hollow article having a flange by utilizing a method of forming materials by plastic deformation.
There are a great variety of hollow articles having flanges at their ends, such as hollow hat-shaped bodies a (having a blind hole) as shown in FIG. 1, and gear blanks o (having through holes) as shown in FIG. 2. Conventional methods for producing these articles are shown in FIGS. 3(I)-3(IV).
The method shown in FIG. 3 for producing a hollow hat-shaped article having a blind hole internally comprises cropping a bar material into a blank d as shown in FIG. 3(I), smoothing both ends thereof and providing the blank with a tapered surfaces e as shown in FIG. 3(II), providing by swaging a flange part f as shown in FIG. 3(III), and forming the outside of a hollow part g and the internal hole h therein as shown in FIG. 3(IV) by forcing a mandrel into the hole h. This method requires not only four steps of operation, inclusive of one for material cropping into a blank, but also a great force in piercing the mandrel into the blank for press-forming the hollow part g. This force is applied through an area not wider than the cross-sectional area of the mandrel, thus entailing disadvantageous features such as buckling of the mandrel and shortening of the operational life of the same. Although there are methods for drilling and shaping the internal bore, these methods are not suitable for quantity or mass production and for reasons of economy.